Narrow Results

The growth mechanisms of GaAs nanowhiskers (NWs) during molecular beam epitaxy (MBE) are studied theoretically and experimentally. A kinetic model of the diffusion-induced NW growth is presented that allows one to predict the dependence of NW length on the drop radius and on the technologically controlled MBE growth conditions. The results of scanning electron microscopy studies of GaAs NWs grown at different conditions on the GaAs(111)B surface activated by Au are presented and analyzed. It is shown that the length of NWs increases with decreasing the drop radius and with decreasing the deposition rate of GaAs, while its temperature dependence has a certain maximum. The aspect ratio of MBE-grown GaAs NWs is higher than 100. The maximum length of NWs is several times larger than the effective thickness of the deposited GaAs. The obtained results demonstrate that the NW growth is controlled by the adatom diffusion toward their tip rather than by the adsorption-induced vapor–liquid–solid mechanism. The growth conditions' influence on the NW morphology may be used for the controlled fabrication of NWs by MBE for different applications.

The effect of ultraviolet, visible and near-infrared irradiation on the yield and morphology of single crystalline C₆₀ fullerene nanowhiskers (FNWs) and nanotubes (FNTs) was investigated in an effort to produce large-scale quantities of FNWs and FNTs. These fullerene nanomaterials were synthesized by the liquid–liquid interfacial precipitation method using pyridine and isopropyl alcohol (IPA) as solvents. The C₆₀–pyridine solution was illuminated using different wavelengths for 24 h at ambient pressure and temperature before addition of IPA. High yields (30–38 mg/L) were obtained upon irradiation using wavelengths in the ultraviolet region in accordance with the increased photoabsorption signal of solid C₆₀ and C₆₀ dissolved in pyridine acquired by a UV-VIS-NIR spectrophotometer. However, elevated yields (21–27 mg/L) were also obtained in the 600–800 nm regions, where C₆₀ absorption is particularly weak. Such an enhanced yield of FNTs and FNWs is probably related to the reported rise in transient absorption of the triplet excited state of C₆₀ in the 740 nm region formed by the decay of the photoexcited singlet C₆₀ through intersystem crossing. The formation of photopolymerized fullerene nanofibers was also observed by Raman spectroscopy, it is attributed to ultraviolet and visible light irradiation. SEM and TEM observations suggest that preparation of FNWs and FNTs by irradiation using different wavelengths of light does not produce apparent morphological transformations on the surface of these fullerene materials.

Two types of ferrocene(Fc)-doped C₆₀ nanowhiskers [C₆₀/Fc NWs and C₆₀/ferrocene pyrrolidine-C₆₀(C₆₀-Fc) NWs] were prepared by the liquid–liquid interfacial precipitation method using toluene solution of C₆₀ and Fc or C₆₀-Fc and isopropyl alcohol (IPA). The morphology of C₆₀ precipitates was remarkably changed by the addition of Fc or C₆₀-Fc to the C₆₀ toluene solution. The scanning TEM mapping analysis of C₆₀/Fc NWs showed that the intensity of ferrocene is high at the edge, indicating that ferrocene covers the outside surface of the NWs. In the case of C₆₀/C₆₀-Fc NWs, however, the scanning TEM mapping analysis showed that C₆₀-Fc disperses well in the NWs.

Fe-decorated fullerene nanowhiskers were prepared by using the liquid–liquid interfacial precipitation method. The prepared nanowhiskers were characterized using scanning electron microscopy (SEM), scanning transmission electron microscopy (STEM), X-ray diffraction (XRD) and Raman spectroscopy. Formation of both tubular and nontubular nanowhiskers was observed with fine dispersion of Fe ions. The XRD and Raman-spectroscopic studies showed the fcc crystalline nature and polymerization of the nanowhiskers, respectively. The results were compared with Ce- and Ni-incorporated fullerene nanowhiskers.